This invention relates to an apparatus and method for continuously measuring a polarizing property such as an optical axis direction and a light absorbing direction of a polarizing material, and, more particularly, it relates to an apparatus and method for continuously measuring an optical axis direction of a transparent specimen in the respective positions in the longitudinal direction.
For measurement of an optical axis direction of a transparent specimen, as shown in FIG. 1, the prior art has heretofore proposed to employ an orthogonal Nicol optical system which consists of a light source 1, two polarizers 3a, 3b disposed to intersect optical axes thereof with each other, and a light receptor 4 to insert a specimen 2 in a chip form to be measured between both the polarizers 3a, 3b. The surfaces of the specimen intersect with the axis of the optical system at a right angle. The specimen is rotated around the axis of the optical axis, thereby determining the optical axis of the specimen in accordance with a relationship between its rotational angle and an intensity of the light passing through the optical system. If the specimen is elongated and the optical axis direction is varied in the respective positions in the longitudinal direction, such a conventional apparatus is required not only to cut the specimen into segments in a moderate length in order to determine the optical axis direction in the respective positions but also to measure the optical axis direction of every segment. This will cause much labor and time to be consumed.
In the prior art apparatus, as shown in FIG. 1A the apparatus is designed so that a cover 7 is mounted adjacent the holder 5 on a casing 6 which acts to prevent the light from entering from outside, and that the cover 7 is opened to operate the holder for its rotation in measuring. This will render the light easy to enter, thereby causing an inaccurate measurement. This will also require the cover to open and close whenever the holder 5 is rotated, thereby causing difficulty in operation to eventually render measurement insufficient.
Various apparatus have been heretofore proposed and suggested to measure the angle of deviation from the absorption axis of each of various polarizers and to examine quality but failed in providing a desirable apparatus. At the experimental level, an apparatus as shown in FIG. 1B has been well known. More specifically, as seen from FIG. 1B, a polarizer plate 83 as a specimen to be measured is held between two polarizers 81, 82 whose absorption axes are intersected with each other. The light of a fluorescent lamp 84 or the like is transmitted from one side to the polarizers to rotate only the polarizer plate 83 while being observed by the naked eye 84'. When the transmissive light is most lowered, the angle of displacement from the polarizer plate 83 may be obtained by measuring with a protractor an angle defined by one side of the polarizer plate 83 and either one of the polarizers 81, 82. However, as disadvantages derived from the prior art, it is necessary to limit a measurement to one point, it is impossible to conduct a continuous measurement, and it is impossible to conduct a measurement of an accurate and fine angle of displacement.
Also, various methods have been therefore proposed and suggested to measure an angle of displacement or deviation from the absorption axis each of various polarizers but not succeeded in obtaining an established method. Various polarizers are indispensable to a display apparatus, especially, to a display apparatus for use with a liquid crystal. For such application, should an axis of a polarizer be displaced, a transmittivity of visual light is out of a specification limit. Furthermore, a problem of uneveness in color and the like arises from the polarizer assembled into a cell.